Czichos H., Saito T., Smith L.E. (Eds.) Handbook of Metrology and Testing

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18 Part A Fundamentals of Metrology and Testing

Matter

Materials

Processing

Manufacturing

Machining

Forming

Nanotechnology

assembly

• Solids

• Liquids

• Molecules

• Atoms

• Structural materials

Mechanical, thermal tasks

• Functional materials

Electrical, magnetic, optical tasks

• Smart materials

Sensors and actuator tasks

Fig. 1.13 Materials and their characteristics result from the processing of matter

Mechanical properties Electrical properties Thermal properties

Elastic modulus E Specific resistance Thermal conductivity

Metals Metals Inorganics Organics Metals Inorganics Organics

–2

–4

–6

–8

–1

–2

Osmium

Tungsten

Chromium

Steel

Copper

Gold

Lead

Silver

Tin

Ceramics

Limit:

Diamond

SiC

Glass

Mullite

Porcelain

Concrete

Timber

Rubber

PVC

PMMA

Epoxy

PTFE

Steel

Copper

Silver

Glass

Epoxy

PVC

PTFE

Porcelain

Mullite

Cermets

Graphite

Con-

ductive

polymers

(GPa)

(Ω m)

–1

5×10

Ceramics

SiC

Glass

Porcelain

Silica

Silver

Copper

Gold

Aluminum

Tungsten

Chromium

Bronze

Lead

Steel

(W/(m K))

Concrete

Epoxy

PVC

PTFE

Timber

Inorganics

Organics

Aluminum

Fig. 1.14 Overview of mechanical, electrical, and thermal materials properties for the basic types of materials (metal,

inorganic, or organic)

Part A 1.3

Introduction to Metrology and Testing 1.3 Fundamentals of Materials Characterization 19

numerical spectra of some mechanical, electrical, and

thermal properties of metals, inorganics, and organics is

showninFig.1.14 [1.16].

It must be emphasized that the numerical ranking of

materials in Fig. 1.14 is based on rough, average val-

ues only. Precise data of materials properties require the

speciﬁcation of various inﬂuencing factors described

above and symbolically expressed as

Materials properties data

= f (composition–microstructure–scale,

external loading,...) .

1.3.5 Performance of Materials

For the application of materials as constituents of

engineered products, performance characteristics such

as quality, reliability, and safety are of special im-

portance. This adds performance control and material

failure analysis to the tasks of application-oriented ma-

terials measurement, testing, and assessment. Because

all materials interact with their environment, materials–

environment interactions and detrimental inﬂuences on

Materials–environment interactions

•Ores

• Natural substances

• Coal • Oil

• Chemicals

Raw materials

• Metals • Polymers

• Ceramics • Composites

• Structural materials

• Functional materials

Engineering materials

End of use

Deposition

Processing

Products

systems

• Scrap

• Waste

•Refuse

Materials

integrity

control

• Aging

• Biodegradation

• Corrosion

•Wear

• Fracture

Functional loads

The

Earth

Matter

Recycling

Performance

Fig. 1.15 The materials cycle of all products and technical systems

the integrity of materials must also be considered. An

overview of the manifold aspects to be recognized in the

characterization of materials performance is provided in

Fig. 1.15.

The so-called materials cycle depicted schemati-

cally in Fig. 1.15 applies to all manmade technical

products in all branches of technology and econ-

omy. The materials cycle illustrates that materials

(accompanied by the necessary ﬂow of energy and in-

formation) move in cycles through the technoeconomic

system: from raw materials to engineering materials

and technical products, and ﬁnally, after the termina-

tion of their task and performance, to deposition or

recycling.

The operating conditions and inﬂuencing factors

for the performance of a material in a given applica-

tion stem from its structural tasks and functional loads,

as shown in the right part of Fig. 1.15. In each appli-

cation, materials have to fulﬁl technical functions as

constituents of engineered products or parts of tech-

nical systems. They have to bear mechanical stresses

and are in contact with other solid bodies, aggressive

gases, liquids or biological species. In their functional

tasks, materials always interact with their environment,

Part A 1.3

20 Part A Fundamentals of Metrology and Testing

Mechanical

Thermal Radiological Chemical Biological Tribological

Fracture

Aging

Corrosion

Biodeterioration

Wear

Stress

corrosion

Heat

Ionizing

radiation

Gases

Liquids

Micro-

orga-

nisms

High-T-

corrosion

Influences on materials integrity, leading eventually to materials deterioration

Shear

Bending

Torsion

Fretting fatigue

Sliding

Rolling

Tension

Compression

Example: Corroded pipe

Example: Fractured steel rail, broken under the complex combination

of various loading actions: mechanical (local impulse bending), thermal

(temperature variations), chemical (moisture), and tribological (cyclic

rolling, Hertzian wheel-contact pressure, interfacial microslip)

Spin

Impact

Fig. 1.16 Fundamentals of materials performance characterization: inﬂuencing phenomena

so these aspects also have to be recognized to character-

ize materials performance.

For the proper performance of engineered mater-

ials, materials deterioration processes and potential

failures, such as materials aging, biodegradation, corro-

sion, wear, and fracture, must be controlled. Figure 1.16

shows an overview of inﬂuences on materials integrity

and possible failure modes.

Figure 1.16 illustrates in a generalized, simpliﬁed

manner that the inﬂuences on the integrity of materials,

which are essential for their performance, can be cate-

gorized in mechanical, thermal, radiological, chemical,

biological, and tribological terms. The basic materials

deterioration mechanisms, as listed in Fig. 1.15, are ag-

ing, biodegradation, corrosion, wear, and fracture.

The deterioration and failure modes illustrated in

Fig. 1.16 are of different relevance for the two ele-

mentary classes of materials, namely organic materials

and inorganic materials (Fig. 1.8). Whereas aging and

biodegradation are main deterioration mechanisms for

organic materials such as polymers, the various types of

corrosion are prevailing failure modes of metallic mater-

ials. Wear and fracture are relevant as materials deterio-

ration and failure mechanisms for all types of materials.

1.3.6 Metrology of Materials

The topics of measurement and testing applied to ma-

terials (in short metrology of materials) concern the

accurate and ﬁt-for-purpose determination of the behav-

ior of a material throughout its lifecycle.

Recognizing the need for a sound technical basis

for drafting codes of practice and speciﬁcations for ad-

vanced materials, the governments of countries of the

Economic Summit (G7) and the European Commis-

sion signed a Memorandum of Understanding in 1982

to establish the Versailles Project on Advanced Mater-

ials and Standards (VA M A S , http://www.vamas.org/).

This project supports international trade by enabling

scientiﬁc collaboration as a precursor to the drafting

of standards. Following a suggestion of VA M A S ,the

Comité International des Poids et Mesures (CIPM,

Fig. 1.6) established an ad hoc Working Group on the

Metrology Applicable to the Measurement of Material

Properties. The ﬁndings and conclusions of the Work-

ing Group on Materials Metrology were published in

a special issue of Metrologia [1.17]. One important ﬁnd-

ingistheconﬁdence ring for traceability in materials

metrology (Fig. 1.4).

Part A 1.3

Introduction to Metrology and Testing 1.3 Fundamentals of Materials Characterization 21

Materials

application

Processing and

synthesis of matter

Engineering design,

production technologies

Functional

loads

Deterioration

actions

Reference materials

Reference methods

Reference methods,

nondestructive evaluation

Material

Metrology and testing

Composition

Microstructure

Properties

Performance

Environment

Fig. 1.17 Characteristics of materials to be recognized in metrology and testing

Materials in engineering design have to meet one

or more structural, functional (e.g., electrical, optical,

magnetic) or decorative purposes. This encompasses

materials such as metals, ceramics, and polymers, re-

sulting from the processing and synthesis of matter,

based on chemistry, solid-state physics, and surface

physics. Whenever a material is being created, devel-

oped or produced, the properties or phenomena that

the material exhibits are of central concern. Experience

shows that the properties and performance associated

with a material are intimately related to its composi-

tion and structure at all scale levels, and inﬂuenced

also by the engineering component design and produc-

tion technologies. The ﬁnal material, as a constituent

of an engineered component, must perform a given

task and must do so in an economical and societally

acceptable manner. All these aspects are compiled in

Fig. 1.17 [1.15].

The basic groups of materials characteristics essen-

tially relevant for materials metrology and testing, as

shown in the central part of Fig. 1.17, can be categorized

as follows.

•

Intrinsic characteristics are the material’s com-

position and material’s microstructure, described

in Sect. 1.3.1. The intrinsic (inherent) materials

characteristics result from the processing and syn-

thesis of matter. Metrology and testing to determine

these characteristics have to be backed up by suit-

able reference materials and reference methods, if

available.

•

Extrinsic characteristics are the material’s prop-

erties and material’s performance, outlined in

Sects. 1.3.4 and 1.3.5. They are procedural charac-

teristics and describe the response of materials and

engineered components to functional loads and en-

vironmental deterioration of the material’s integrity.

Metrology and testing to determine these character-

istics have to be backed up by suitable reference

methods and nondestructive evaluation (NDE).

It follows that, in engineering applications of mater-

ials, methods and techniques are needed to characterize

intrinsic and extrinsic material attributes, and to con-

sider also structure–property relations. The methods

and techniques to characterize composition and mi-

crostructure are treated in part B of the handbook. The

methods and techniques to characterize properties and

performance are treated in parts C and D. The ﬁnal

part E of the handbook presents important modeling and

simulation methods that underline measurement pro-

cedures that rely on mathematical models to interpret

complex experiments or to estimate properties that can-

not be measured directly.

Part A 1.3

22 Part A Fundamentals of Metrology and Testing

References

1.1 BIPM: International Vocabulary of Metrology,

3rd edn. (BIPM, Paris 2008), available from

http://www.bipm.org/en/publications/guides/

1.2 C. Ehrlich, S. Rasberry: Metrological timelines in

traceability, J. Res. Natl. Inst. Stand. Technol. 103,

93–106 (1998)

1.3 EUROLAB: Measurement uncertainty revisited: Al-

ternative approaches to uncertainty evaluation,

EUROLAB Tech. Rep. No. 1/2007 (EUROLAB, Paris 2007),

http://www.eurolab.org/

1.4 ISO: Guide to the Expression of Uncertainty in Mea-

surement (GUM-1989) (International Organization

for Standardization, Geneva 1995)

1.5 P. Howarth, F. Redgrave: Metrology – In Short,3rd

edn. (Euramet, Braunschweig 2008)

1.6 ISO Guide 30: Terms and Deﬁnitions of Reference

Materials (International Organization for Standard-

ization, Geneva 1992)

1.7 T. Adam: Guide for the Estimation of Measurement

Uncertainty in Testing (American Association for Lab-

oratory Accreditation (A2LA), Frederick 2002)

1.8 EUROLAB: Guide to the evaluation of measurement

uncertainty for quantitative tests results, EURO-

LAB Tech. Rep. No. 1/2006 (EUROLAB, Paris 2006),

http://www.eurolab.org/

1.9 EURACHEM/CITAC Guide: Quantifying Uncertainty in

Analytical Measurement, 2nd edn. (EURACHEM/CITAC,

Lisbon 2000)

1.10 B. Magnusson, T. Naykki, H. Hovind, M. Krysell:

Handbook for Calculation of Measurement. Un-

certainty, NORDTEST Rep. TR 537 (Nordtest, Espoo

2003)

1.11 R. Cook: Assessment of Uncertainties of Measurement

for Calibration and Testing Laboratories (National

Association of Testing Authorities Australia, Rhodes

2002)

1.12 J. Ma, I. Karaman: Expanding the repertoire of

shape memory alloys, Science 327, 1468–1469

(2010)

1.13 S. Bennett, G. Sims: Evolving needs for metrology in

material property measurements – The conclusions

of the CIPM Working Group on Materials Metrology,

Metrologia 47,1–17(2010)

1.14 M.F. Ashby, Y.J.M. Brechet, D. Cebon, L. Salvo: Se-

lection strategies for materials and processes, Mater.

Des. 25, 51–67 (2004)

1.15 H. Czichos: Metrology and testing in mater-

ials science and engineering, Measure 4,46–77

(2009)

1.16 H. Czichos, B. Skrotzki, F.-G. Simon: Materials. In:

HÜTTE – Das Ingenieurwissen, 33rd edn., ed. by

H. Czichos, M. Hennecke (Springer, Berlin, Heidel-

berg 2008)

1.17 S. Bennett, J. Valdés (Eds.): Materials metrology,

Foreword, Metrologia 47(2) (2010)

Part A 1

Metrology Pri

2. Metrology Principles and Organization

This chapter describes the basic elements of

metrology, the system that allows measurements

made in different laboratories to be conﬁdently

compared. As the aim of this chapter is to give an

overview of the whole ﬁeld, the development of

metrology from its roots to the birth of the Me-

tre Convention and metrology in the 21st century is

given.

2.1 The Roots and Evolution of Metrology .... 23

2.2 BIPM: The Birth of the Metre Convention 25

2.3 BIPM: The First 75 Years......................... 26

2.4 Quantum Standards:

A Metrological Revolution...................... 28

2.5 Regional Metrology Organizations.......... 29

2.6 Metrological Traceability ....................... 29

2.7 Mutual Recognition of NMI Standards:

The CIPM MRA ....................................... 30

2.7.1 The Essential Points of the MRA...... 30

2.7.2 The Key Comparison Database

(KCDB)......................................... 31

2.7.3 Take Up of the CIPM MRA ............... 31

2.8 Metrology in the 21st Century................. 32

2.8.1 Industrial Challenges .................... 32

2.8.2 Chemistry, Pharmacy, and Medicine 33

2.8.3 Environment, Public Services,

and Infrastructures....................... 34

2.9 The SI System and New Science .............. 34

References .................................................. 37

2.1 The Roots and Evolution of Metrology

From the earliest times it has been important to com-

pare things through measurements. This had much to

do with fair exchange, barter, or trade between commu-

nities, and simple weights such as the stone or measures

such as the cubit were common. At this level, parts of

the body such as hands and arms were adequate for

most needs. Initially, wooden length bars were easy to

compare and weights could be weighed against each

other. Various forms of balance were commonplace in

early history and in religion. Egyptian tomb paintings

show the Egyptian god Anubis weighing the soul of

the dead against an ostrich feather – the sign of purity

(Fig. 2.1). Noah’s Ark was, so the Book of Genesis re-

ports, 300 cubits long by 50 cubits wide and 30 cubits

high. No one really knows why it was important to

record such details, but the Bible, as just one example,

is littered with metrological references, and the symbol-

ism of metrology was part of early culture and art.

A steady progression from basic artifacts to natu-

rally occurring reference standards has been part of the

entire history of metrology. Metrologists are familiar

with the use of the carob seed in early Mediterranean

civilizations as a natural reference for length and for

weight and hence volume. The Greeks were early

traders who paid attention to metrology, and they were

known to keep copies of the weights and measures of

the countries with which they traded.

Fig. 2.1 Anubis

Part A 2

24 Part A Fundamentals of Metrology and Testing

Fig. 2.2 Winchester yard

Fig. 2.3 Imperial length standards, Trafalgar Square, London

The Magna Carta of England set out a framework for

a citizen’s rights and established one measure through-

out the land. Kings and queens took interest in national

weights and measures; Fig. 2.2 shows the Winchester

yard, the bronze rod that was the British standard from

1497 to the end of the 16th century. The queen’s mark

we see here is that of Elizabeth the First (1558–1603).

In those days, the acre was widely used as a measure-

ment, derived from the area that a team of oxen could

plow in a day. Plowing an acre meant that you had to

walk 66 furlongs, a linear dimension measured in rods.

The problem with many length measurements was

that the standard was made of the commonly available

metals brass or bronze, which have a fairly large co-

efﬁcient of expansion. Iron or steel measures were not

developed for a couple of centuries. Brass and bronze

therefore dominated the length reference business un-

til the early 19th century, by which time metallurgy had

developed enough – though it was still something of

a black art – for new, lower-expansion metals to be used

and reference temperatures quoted. The UK imperial

references were introduced in 1854 and reproduced in

Trafalgar Square in the center of London (Fig. 2.3), and

the British Empire’s domination of international com-

merce saw the British measurement system adopted in

many of its colonies.

In the mid 18th century, Britain and France com-

pared their national measurement standards and realized

that they differed by a few percent for the same unit.

Although the British system was reasonably consistent

throughout the country, the French found that differ-

ences of up to 50% were common in length measurement

within France. The ensuing technical debate was the start

of what we now accept as the metric system. France led

the way, and even in the middle of the French Revolution

the Academy of Science was asked to deduce an invari-

able standard for all the measures and all the weights.

The important word was invariable. There were two op-

tions available for the standard of length: the second’s

pendulum and the length of the Earth’s meridian. The ob-

vious weakness of the pendulum approach was that its

period depended on the local acceleration due to grav-

ity. The academy therefore chose to measure a portion

of the Earth’s circumference and relate it to the ofﬁcial

French meter. Delambre and Méchain, who were en-

trusted with a survey of the meridian between Dunkirk

and Barcelona, created the famous Mètre des Archives,

a platinum end standard.

The international nature of measurement was driven,

just like that of the Greek traders of nearly 2000 years

before, by the need for interoperability in trade and ad-

vances in engineering measurement. The displays of

brilliant engineering at the Great Exhibitions in London

and Paris in the 19th century largely rested on the ability

to measure well. The British Victorian engineer Joseph

Whitworth coined the famous phrase you can only make

as well as you can measure and pioneered accurate screw

threads. He immediately saw the potential of end stan-

dard gages rather than line standards where the reference

length was deﬁned by a scratch on the surface of a bar.

The difﬁculty, he realized, with line standards was that

optical microscopes were not then good enough to com-

pare measurements of line standards well enough for the

best precision engineering. Whitworth was determined

to make the world’s best measuring machine. He con-

structed the quite remarkable millionth machine based

on the principle that touch was better than sight for preci-

sion measurement. It appears that the machine had a feel

of about 1/10 of a thousandth of an inch. Another inter-

esting metrological trend at the 1851 Great Exhibition

was military: the word calibrate comes from the need to

control the caliber of guns.

Part A 2.1

Metrology Principles and Organization 2.2 BIPM: The Birth of the Metre Convention 25

At the turn of the 19th century, many of the industri-

alized countries had set up national metrology institutes,

generally based on the model established in Germany

with the Physikalisch Technische Reichsanstalt, which

was founded in 1887. The economic beneﬁts of such

a national institute were immediately recognized, and as

a result, scientiﬁc and industrial organizations in a num-

ber of industrialized countries began pressing their gov-

ernments to make similar investments. In the UK, the

British Association for the Advancement of Science re-

ported that, without a national laboratory to act as a focus

for metrology, the country’s industrial competitiveness

wouldbeweakened.Thecausewastakenupmore widely,

and the UK set up the National Physical Laboratory

(NPL) in 1900. The USA created the National Bureau of

Standards in 1901 as a result of similar industrial pres-

sure. The major national metrology institutes (NMIs),

however, had a dual role. In general, they were the main

focus for national research programs on applied physics

and engineering. Their scientiﬁc role in the development

of units – what became the International System of Units,

the SI – began to challenge the role of the universities in

the measurement of fundamental constants. This was es-

pecially true after the development of quantum physics in

the 1920s and 1930s. Most early NMIs therefore began

with two major elements to their mission

•

a requirement to satisfy industrial needs for accurate

measurements, through standardization and veriﬁca-

tion of instruments; and

•

determination of physical constants so as to improve

and develop the SI system.

The new industries which emerged after the First World

War made huge demands on metrology and, together

with mass production and the beginnings of multina-

tional production sites, raised new challenges which

brought NMIs into direct contact with companies, so

causing a close link to develop between them. At that

time, and even up to the mid 1960s, nearly all cali-

brations and measurements that were necessary for in-

dustrial use were made in the NMIs,andinthegage

rooms of the major companies, as were most measure-

ments in engineering metrology. The industries of the

1920s, however, developed a need for electrical and opti-

cal measurements, so NMIs expanded their coverage and

their technical abilities.

The story since then is one of steady technical ex-

pansion until after the Second World War. In the 1950s,

though, there was renewed interest in a broader ap-

plied focus for many NMIs so as to develop civilian

applications for much of the declassiﬁed military tech-

nology. The squeeze on public budgets in the 1970s

and 1980s saw a return to core metrology, and many

other institutions, public and private, took on the re-

sponsibility for developing many of the technologies,

which had been initially fostered at NMIs. The NMIs

adjusted to their new roles. Many restructured and

found new, often improved, ways of serving indus-

trial needs. This recreation of the NMI role was also

shared by most governments, which increasingly saw

them as tools of industrial policy with a mission to

stimulate industrial competitiveness and, at the end of

the 20th century, to reduce technical barriers to world

trade.

2.2 BIPM: The Birth of the Metre Convention

A brief overview of the Metre Convention has already

been given in Sect. 1.2.1. In the following, the historical

development will be described.

During the 1851 Great Exhibition and the 1860

meeting of the British Association for the Advance-

ment of Science (BAAS), a number of scientists and

engineers met to develop the case for a single system

of units based on the metric system. This built on the

early initiative of Gauss to use the 1799 meter and

kilogram in the Archives de la République, Paris and

the second, as deﬁned in astronomy, to create a co-

herent set of units for the physical sciences. In 1874,

the three-dimensional CGS system, based on the cen-

timeter, gram, and second, was launched by the BAAS.

However, the size of the electrical units in the CGS sys-

tem were not particularly convenient and, in the 1880s,

the BAAS and the International Electrotechnical Com-

mission (IEC) approved a set of practical electrical units

based on the ohm, the ampere, and the volt. Parallel to

this attention to the units, a number of governments set

up what was then called the Committee for Weights and

Money, which in turn led to the 1870 meeting of the

Commission Internationale du Mètre. Twenty-six coun-

tries accepted the invitation of the French Government

to attend; however, only 16 were able to come as the

Franco–Prussian war intervened, so the full commit-

tee did not meet until 1872. The result was the Metre

Convention and the creation of the Bureau International

Part A 2.2

26 Part A Fundamentals of Metrology and Testing

Fig. 2.4 Bureau International des Poids et Mesures, Sévres

des Poids et Mesures (BIPM, International Bureau of

Weights and Measures), in the old Pavillon de Breteuil

at Sèvres (Fig. 2.4), as a permanent scientiﬁc agency

supported by the signatories to the convention. As this

required the support of governments at the highest level,

the Metre Convention was not ﬁnally signed until 20

May 1875.

The BIPM’s role was to establish new metric stan-

dards, conserve the international prototypes (then the

meter and the kilogram) and to carry out the compar-

isons necessary to assure the uniformity of measures

throughout the world. As an intergovernmental, diplo-

matic treaty organization, the BIPM was placed under

the authority of the General Conference on Weights

and Measures (CGPM). A committee of 18 scientiﬁc

experts, the International Committee for Weights and

Measures (CIPM), now supervises the running of the

BIPM. The aim of the CGPM and the CIPM was, and

still is, to assure the international uniﬁcation and de-

velopment of the metric system. The CGPM now meets

every 4 years to review progress, receive reports from

the CIPM on the running of the BIPM, and establish the

operating budget of the BIPM, whereas the CIPM meets

annually to supervise the BIPM’s work.

When it was set up, the staff of the BIPM con-

sisted of a director, two assistants, and the necessary

number of employees. In essence, then, a handful of

people began to prepare and disseminate copies of

the international prototypes of the meter and the kilo-

gram to member states. About 30 copies of the meter

and 40 copies of the prototype kilogram were dis-

tributed to member states by ballot. Once this was

done, some thought that the job of the BIPM would

simply be that of periodically checking (in the jar-

gon, verifying) the national copies of these standards.

This was a short-lived vision, as the early investiga-

tions immediately showed the importance of reliably

measuring a range of quantities that inﬂuenced the

performance of the international prototypes and their

copies. As a result, a number of studies and projects

were launched which dealt with the measurement of

temperature, density, pressure, and a number of related

quantities. The BIPM immediately became a research

body, although this was not recognized formally until

1921.

Returning to the development of the SI, one of the

early decisions of the CIPM was to modify the CGS

system to base measurements on the meter, kilogram,

and second – the MKS system. In 1901, Giorgi showed

that it was possible to combine the MKS system with

the practical electrical units to form a coherent four-

dimensional system by adding an electrical unit and

rewriting some of the equations of electromagnetism in

the so-called rationalized form. In 1946, the CIPM ap-

proved a system based on the meter, kilogram, second,

and ampere – the MKSA system. Recognizing the am-

pere as a base unit of the metric system in 1948, and

adding, in 1954, units for thermodynamic temperature

(the kelvin and luminous intensity (the candela), the

11th CGPM in 1960 coined the name Système inter-

nationale d’Unités, the SI. At the 14th CGPM in 1971,

the present-day SI system was completed by adding the

mole as the base unit for the amount of substance, bring-

ing the total number of base units to seven. Using these

base units, a hierarchy of derived units and quantities of

the SI have been developed for most, if not all, measure-

ments needed in today’s society. A substantial treatment

of the SI is to be found in the 8th edition of the SI

brochure published by the BIPM [2.1].

2.3 BIPM: The First 75 Years

After its intervention in the initial development of the

SI,theBIPM continued to develop fundamental metro-

logical techniques in mass and length measurement but

soon had to react to the metrological implications of

major developments in atomic physics and interferom-

etry. In the early 1920s, Albert Michelson came to

work at the BIPM and built an eponymous interfer-

ometer to measure the meter in terms of light from

Part A 2.3

Metrology Principles and Organization 2.3 BIPM: The First 75 Years 27

the cadmium red line – an instrument which, although

modiﬁed, did sterling service until the 1980s. In tem-

perature measurement, the old hydrogen thermometer

scale was replaced with a thermodynamic-based scale

and a number of ﬁxed points. After great debate, elec-

trical standards were added to the work of the BIPM in

the 1920s with the ﬁrst international comparisons of re-

sistance and voltage. In 1929, an electrical laboratory

was added, and photometry arrived in 1939.

In these early days, it was clear that the BIPM

needed to ﬁnd a way of consulting and collaborating

with the experts in the world’s NMIs. The solution

adopted is one which still exists and ﬂourishes today.

The best way of working was in face-to-face meetings,

so the concept of a consultative committee to the CIPM

was born. Members of the committee were drawn from

experts active in the world’s NMIsandmettodeal

with matters concerning the deﬁnitions of units and the

techniques of comparison and calibration. The consul-

tative committees are usually chaired by a member of

the CIPM. Much information was shared, although for

obvious logistical reasons, the meetings were not too

frequent. Over the years, the need for new consulta-

tive committees grew in reaction to the expansion of

metrology, and now 10 consultative committees exist,

with over 25 working groups.

The CIPM is rightly cautious about establishing

a new committee, but proposals for new ones are con-

sidered from time to time, usually after an initial survey

through a working group. In the last 10 years, joint com-

mittees have been created to tackle issues such as the

Table 2.1 List of consultative committees with dates of formation

Names of consultative committees and the date of their formation

(Names of consultative committees have changed as they have gained new responsibilities;

the current name is cited)

Consultative Committee for Electricity and Magnetism, CCEM (1997, but created in 1927)

Consultative Committee for Photometry and Radiometry, CCPR (1971 but created in 1933)

Consultative Committee for Thermometry, CCT (1937)

Consultative Committee for Length, CCL (1997 but created in 1952)

Consultative Committee for Time and Frequency, CCTF (1997, but created 1956)

Consultative Committee for Ionizing Radiation, CCRI (1997, but created in 1958)

Consultative Committee for Units, CCU (1964, but replacing a similar commission created in 1954)

Consultative Committee for Mass and Related Quantities, CCM (1980)

Consultative Committee for Amount of Substance and Metrology in Chemistry, CCQM (1993)

Consultative Committee for Acoustics, Ultrasound, and Vibration, CCAUV (1999)

international approach to the estimation of measure-

ment uncertainties or to the establishment of a common

vocabulary for metrology. Most of these joint com-

mittees bring the BIPM together with international or

intergovernmental bodies such as the International Or-

ganization for Standardization (ISO), the International

Laboratory Accreditation Cooperation (ILAC), and the

IEC. As the work of the Metre Convention moves

into areas other than its traditional activities in physics

and engineering, joint committees are an excellent way

of bringing the BIPM together with other bodies that

bring specialist expertise – an example being the joint

committee for laboratory medicine, established recently

with the International Federation of Clinical Chemists

and the ILAC.

The introduction of ionizing radiation standards to

theworkoftheBIPM came when Marie Curie de-

posited her ﬁrst radium standard at the BIPM in 1913.

As a result of pressure, largely from the USSR delega-

tion to the CGPM,theCIPM took the decision to deal

with metrology in ionizing radiation.

In the mid 1960s, and at the time of the expansion

into ionizing radiation, programs on laser length mea-

surement were also started. These contributed greatly to

the redeﬁnition of the meter in 1983. The BIPM also

acted as the world reference center for laser wavelength

or frequency comparisons in much the same was as it

did for physical artifact-based standards. In the mean-

time, however, the meter bar had already been replaced,

in 1960, by an interferometric-based deﬁnition using

optical radiation from a krypton lamp.

Part A 2.3